A nuclear Iran, he added, is "a real threat to Israeli security, ours and our allies', and that is why we are determined to prevent this from happening."

News reports of American uncertainty regarding Israel’s intentions in confronting the Iranian threat, particularly after a revealing IAEA report about Iran’s covert weapons programs was released in early November, have highlighted tensions in the bilateral relationship.

Shapiro also said the U.S. and the Quartet - the EU, Russia, U.S. and the UN - expect direct talks. Representatives from the group are scheduled to meet with Israeli and Palestinian officials next week.

"We emphasize that the parties need to talk directly," the Ambassador said.

Meanwhile, Republican presidential candidates used a Republican Jewish Coalition forum in Washington on Wednesday to denounce the Obama administration’s policies toward the Middle East and pledge a tougher stance towards Iran.

While much of their speeches were devoted to criticism of the Obama administration, the candidates offered their own ideas for the U.S.-Israel relationship and Iran’s nuclear campaign.

Mitt Romney called for "regime change" in Iran, and made clear that the military option was still on the table. He also reiterated a promise that his first foreign trip as president would be to Israel.

Former House Speaker Newt Gingrich said he would aim to sabotage Iran’s oil supply while funding dissident groups. On Israel, he said "there will be an executive order about two hours after the inaugural address. We will send the embassy from Tel Aviv to Jerusalem, as of that day."